The tremor struck at 3.49am at a depth of 608 kilometres.
It was centred 101 kilometres east-southeast of the capital Suva.
The Pacific Tsunami Warning Centre says the earthquake was so deep it is unlikely to make a dangerous tsunami.
There have been no reports of damage.
However, residents in parts of the main island of Viti Levu commented on social media that they were awoken to shaking.